launcher: v0.1 — PhotinoNET shell + multi-version orchestration

Single-download .NET 9 self-contained launcher for hosting / joining
DorkNet servers. Reads versions.json from main to discover supported
client builds, fetches the matching server binary + client patcher
from GitHub Releases per branch, manages the server subprocess +
Cloudflare quick-tunnel, and wraps it all in a PhotinoNET window.

Code layout:
- Program.cs           PhotinoNET window + message bridge bootstrap
- Backend/             AppPaths, AppState, VersionsManifest,
                       ReleaseDownloader, ServerProcess, ClientPatcher,
                       Tunnel, RecRoomPicker, JoinCode, MessageBridge
- ui/                  index.html + style.css + app.js (no build step)
- RELEASES.md          GitHub Releases artifact contract per-version
                       branches must publish to

Per-version branches need to ship two release assets per tag:
- dorknet-server-{version_key}-win-x64.zip
- dorknet-clientpatch-{version_key}.zip
(see launcher/RELEASES.md for the full naming + arg contract)

Photon AppIds, JWT secret, and the picked Rec Room path stay
per-machine; the launcher never bundles them.

launcher/Program.cs

@@ -0,0 +1,70 @@
+using Photino.NET;
+using DorkNet.Launcher.Backend;
+using System.Text.Json;
+
+namespace DorkNet.Launcher;
+
+/// <summary>Entry point + the host↔JS message bridge. The window is a
+/// PhotinoNET wrapper around WebView2, loading ui/index.html from the
+/// app's directory. Every JS ↔ C# call goes through one JSON-tagged
+/// envelope so we can route by command/event name without per-call
+/// glue.</summary>
+public static class Program
+{
+    [STAThread]
+    public static void Main(string[] args)
+    {
+        AppPaths.EnsureDirectoriesExist();
+
+        var indexPath = Path.Combine(AppContext.BaseDirectory, "ui", "index.html");
+        if (!File.Exists(indexPath))
+        {
+            // First-aid: if the UI files didn't ship next to the binary,
+            // the window would be blank with no hint why. Surface the
+            // missing-file path before opening anything.
+            MessageBox.Error(
+                "DorkNet UI files missing",
+                $"Could not find {indexPath}. Reinstall the launcher.");
+            return;
+        }
+
+        var window = new PhotinoWindow()
+            .SetTitle("DorkNet")
+            .SetUseOsDefaultSize(false)
+            .SetSize(900, 640)
+            .SetResizable(true)
+            .Center()
+            .Load(new Uri(indexPath));
+
+        var bridge = new MessageBridge(window);
+        window.RegisterWebMessageReceivedHandler((sender, message) =>
+        {
+            // JS sends JSON envelopes: {"type":"command-name","payload":{...},"requestId":"..."}
+            // Reply path is bridge.SendEvent — fire-and-forget unless requestId is set.
+            try
+            {
+                bridge.HandleAsync(message).GetAwaiter().GetResult();
+            }
+            catch (Exception ex)
+            {
+                bridge.SendEvent("error", new { source = "bridge", message = ex.Message });
+            }
+        });
+
+        window.WaitForClose();
+    }
+}
+
+/// <summary>Minimal MessageBox helper — DorkNet won't pop these often,
+/// but a missing-UI-file failure mode needs a visible signal before the
+/// PhotinoNET window opens.</summary>
+internal static class MessageBox
+{
+    public static void Error(string title, string body)
+    {
+        System.Windows.Forms.MessageBox.Show(
+            body, title,
+            System.Windows.Forms.MessageBoxButtons.OK,
+            System.Windows.Forms.MessageBoxIcon.Error);
+    }
+}